In a few years you will be able to order a transcript of your entire genetic code for less than $1,000. Adults cannot do much to alter their biological lot, but what if parents could examine their unborn child's genome? Without proper guidance, they might decide to take drastic measures—even to end the pregnancy—based on a misguided reading of the genetic tea leaves.

Two different university laboratories have developed tests that will reveal the entirety of a fetus's genetic code using just a blood sample from the mother (or that sample plus a drop of saliva from the father). Prenatal whole-genome sequencing will provide volumes of information beyond the currently available tests for genetic disorders such as Down's syndrome or Tay-Sachs disease—assays that parents now use to decide how to respond to a pregnancy. The three billion units of code furnished in the new tests will also dwarf the relative trickle of information provided by consumer gene-testing services such as 23andMe, which currently look (postnatally) only at perhaps about one million locations in the genome.

Any woman who undergoes such a test will quickly learn that there is no such thing as a perfect baby. Parents will encounter hundreds and, as the science progresses, thousands of instances in which a particular variant of a gene may statistically suggest (but not guarantee) their child's future. Will the child-to-be one day suffer from melanoma or diabetes? What about obsessive-compulsive disorder? Moreover, clues will emerge in whole-genome scans about not only health prospects but personality as well—whether she is likely to become an introvert or be able to carry a tune or star in high school sports. Whole-genome scans will tell parents a story about a particular future for their child—a future that those parents may not be rooting for.

A compelling example of the angst-provoking uncertainties involved has been raised by bioethicist and Scientific American advisory board member Arthur Caplan. What if a test picks up the gene for albinism? Being an albino is not a disabling medical condition, but it can be a social burden. Might that be enough for some parents to consider ending the pregnancy?

Attitudes toward child rearing might also change, as parents wonder whether their kid is just being bad or whether that tantrum is an example of a dysfunctional serotonin transporter gene. Without careful planning, moreover, the new prenatal genetics might rob a child of the freedom to make decisions best left until adulthood—whether or not to learn, for instance, if a mutation predicts the inevitability of Huntington's disease 20 years hence.

A customer of 23andMe can receive information via the Internet about a multifold greater risk of breast cancer or Alzheimer's disease without conferring with a genetics counselor. A similar laissez-faire approach to prenatal whole-genome testing, which might involve the decision to abort a pregnancy based on a personal and possibly inaccurate interpretation of dense and confusing genetic data, could portend tragedy.

Ultimately the U.S. Food and Drug Administration, genome-testing companies and professional societies such as the American Society of Human Genetics will need to develop a comprehensive policy on prenatal whole-genome testing. One option is to require that parents receive a filtered set of information from a genetics counselor. Bioethics scholars affiliated with the National Institutes of Health wrote an analysis last summer that calls on the medical community to develop a guide to the most relevant genomic data for future parents (life-threatening disease risk obviously tops the list). The report also recommends safeguarding the future child's right not to be told about later-in-life disease risk until adulthood.

Unfortunately, there aren't nearly enough trained genetics counselors to handle the coming upsurge in demand for this type of information. And neither physicians nor other health professionals know enough about genomics and its relevance to serve as steady guides. Without access to a much higher level of refined expertise, the secrets of our offspring's genetic code will continue to remain an unnerving cipher—or worse.

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